The present application discloses embodiments directed to wireless access points for use with a wireless local area network (WLAN). In a typical wireless access point (AP), a single or dual band radio component is operated with one or more omnidirectional or directional antennas having moderate gain. The supportable throughput of an AP is typically determined by the antenna coverage pattern combined with the signal rate and modulation type provided by the radio component. With an increase of wireless traffic in a particular coverage area, it is desirable to service more users on a dense client area. It would thus be desirable to increase throughput of an AP. Several approaches have previously been used, including frequency, time, code, and polarization division multiplexing.
With Frequency Division Multiplexing (FDM), a number of signals are combined into a single channel, where each signal is transmitted over a distinct frequency sub-band within the band of the channel. However, FDM is typically limited by the channel availability of the selected wireless network standard. For example, it may be contemplated to mix three channels under the IEEE 802.11 b/g standards with eight channels under the 802.11a standard within a given physical area if co-channel interference could be mitigated. However, if channel coverages are overlapped, the resulting mutual interference imposes a scaling limitation on the network, and no throughput increase can be obtained. Also, interference is high between transmit and receive channels within collocated or nearby radio components due to antenna-to-antenna coupling, multipath interference, and electronics coupling.
With Time Division Multiplexing (TDM), a signal is divided into a number of time segments of short duration. Data from a respective number of signals is modulated into the time segments. However, TDM is limited by standards and only available if supported therein. It may be desirable to use a time-slotted protocol to enhance throughput, but such slotting might fall outside the current standards, such as with 802.11g or 802.11a, for example. While the current standards may limit throughput efficiency, compatibility requirements with the standard precludes the implementation of a TDM system.
With Code Division Multiplexing (CDM), the transmitter encodes the signal with a pseudo-random data sequence, which is also used to decode the signal. CDM can potentially raise channel utilization if suitable power control and other network management functions are imposed. However, the current AP standards do not permit incorporation of such spread spectrum modulation and multiplexing.
With polarization diversity, two separate channels are multiplexed into orthogonal polarizations of a signal carrier, thereby doubling capacity. Polarization diversity has been employed in AP technology, especially for bridges. However, performance suffers in an indoor environment containing metal grids and other multipath and depolarization propagation phenomena. Therefore, polarization diversity is not viable at the present time without employing real-time adaptive combinational techniques.
With Space Division Multiplexing (SDM) a particular coverage area is divided into sectors. In this approach, a space is divided geometrically using directional antenna beams pointed at clients to minimize coverage overlap. The directional beams may be formed electronically or by using separate apertures, as is known in the art. A common implementation is found in sectorized cellular mobile systems. However, such systems rely on large, expensive high-rejection multiplexing filters to separate transmit channels so as to not interfere with receivers on adjacent beams. This is not a suitable approach for WLAN applications due to both size and cost.
None of the above-noted solutions can satisfy the goal of raising throughput while conforming to presently accepted wireless network standards, though FDM suffers from the least number of drawbacks. A preferred solution would enable the transmit and receive channels to reside in a single AP housing along with the respective antennas. However, with such an approach it would be difficult using known techniques to avoid interference of the adjacent or alternate channels used for transmission and reception of signals.